US2498688A

US2498688A - Demodulator and channel separator system

Info

Publication number: US2498688A
Application number: US678703A
Authority: US
Inventors: Lesti Arnold
Original assignee: Federal Telecommunication Laboratories Inc
Current assignee: Federal Telecommunication Laboratories Inc
Priority date: 1946-06-22
Filing date: 1946-06-22
Publication date: 1950-02-28
Anticipated expiration: 1967-02-28
Also published as: BE479963A; ES182457A1; GB636409A

Description

Feb. 28, 1950 A. LEsTn DEMODULATOR AND CHANNEL SEPARATOR SYSTEM Filed June 22, 1946 2 Sheets-Sheefl 1 WNS@ HTTIPNEY Feb. 28, 1950 A. LEsTl 2,498,588

DEMODULATOR AND CHANNEL SEPARATOR SYSTEM Filed June 22, 1946 2 sheets-sheet 2 9. Ik 1 2 5 4 75 /6 7 5 9 10 AMAN@ HIE IH! U/ 14 I I I I I I I I L o' J A/0 /5 20 25 .5o J5 40 45 6o J5 ATTORNEY Patented Feb. 28, 1950 DEMODULATOR AND CHANNEL snrlimrro4 SYSTEM` Arnold Lesti, New York, N. Y., assignor to Federal Telecommunication Laboratories, Inc..

New

York, N. Y., a corporation of Delaware Application June 22, 1946, Serial No. 678,703

7 Claims. 1

This invention relates to a demodulator and channel separator system for multi-channel time modulated pulse communication systems.

In one type of multi-channel time modulated pulse communication system the train of pulses consists of a succession of series oi pulses, each series consisting of amarker signal followed by a number of signal pulses, each signal pulse of a series forming part of a separate signal channel. The time relationship of the signal pulses is varied with respect to their associated marker signal to carry the modulation. It has heretofore been proposed to utilize a cathode ray tube having a plurality of target elements for separating the channels and demodulating the time modulated pulses, as is described for example, in the copendng U. S. application of D. D. Grieg for Multi-channel system, Serial No. 625,650, led October 30, A1945, now Patent No.

2,485,591, granted October 25, 1949. In the afore-l said application, the channel separation and demodulation is accomplished by generating voltage sweeping a beam at a continuous rate of speed across the faces of a plurality of target elements and only turning on the beam at times determined by the pulses, the time modulation of the pulses controlling the amount of a given target element swept by the turned-on beam. According to the present invention, the cathode ray beam is always turned on during operation of the system but the velocity of deflection of the beam is varied so that as the beam is swept across the target elements, it remains on a given target element for a length of time determined by the time modulation of the pulse controlling said sweep. Further in accordance with the present invention, use,is`

made of a push-pull arrangement to produce certain advantages such as the diminution of cross-talk effects, etc.

An object of the present invention is the provision of an improved demodulator system for time modulated pulse systems.

Another object of the present invention is the provision of an improved channel selector and demodulator for multi-channel time modulated pulse systems.

Another object of the present invention is the provision of a demodulation system for time modulated pulses in which use is made of a cathode ray tube.

An advantage of the present invention over the prior art is the increase in output achieved in comparison with the prior `art due to the fact that according to the present invention the transit time of the electron beam, in moving between the target elements, is very fast while there is a delay on the elements themselves. This distinguishes from the prior art in which there is a fairly rapid rate of speed of the beam at all times since the beam moves at a uniform speed. Consequently in the present invention the beam is on the target elements for longer periods than in the systems of the prior art.

Another advantage of the present invention is the reduction of distortion since the system of the present invention is not critical as to the exact position of the beam and is also not critical as to the conguration thereof. Furthermore, the present system is more easily adjusted, is not as critical with regard to drift of the beam from an exact position, and tends to lessen or reduce cross-talk since the target elements are passed so that cross-talk induced in two target elements which are associated in push-pull tends lto cancel itself out.

Other and further objects of the present invention will become apparent and the invention will be best understood from the following description of an embodiment thereof, referencebeing had to the drawings, in which:

Fig. 1 is a schematic and block diagram of a system embodying the present invention; and

Figs. 2 and 3 are sets of curves used in explaining the operation of the system of Fig. l.

Referring now to the drawings, a train of pulses, such as those illustrated in curve A, Fig. 2i, are fed intothe channel selector and demodulator system of Fig. 1. These pulses may consist of a marker signal I, consisting of a double pulse, followed by a succession of signal pulses 2-I0, which in curve A, are shown in their unmodulated position and may be modulated between the limits indicated by the dotted lines on each side of said signal pulses. Each of the signal pulses 2-IIJ forms part of a separate channel. The en,- tire series of pulses II0 is followed by a succession of similar series Iof pulses to form a pulse train. Such pulse trains may be used to modulate a carrier wave and radiated. This wave may be received by any suitable receiver and the lcarrier frequency removed to thereby reproduce the pulses substantially as shown. The pulses may then be f ed to a channel selector and demodulator system, of the type indicated in Fig. 1, with the pulses being fed in along line I I in said figure.

The marker signal I is selected by a marker selector I2, which may be of the type indicated in said copending application and the output of marker selector I2 is used to synchronize a synchronized pulse generator I3 -toproduce in re,-

paired together as indicated at 35 and connected curve C of Fig. 2. These vcombined'pulsesv are `v then -fed to an integrating network I6 to produce l a voltage Wave I'I, as illustrated in'curve D,'Fig-.B.` 1`

The stepped voltage wave I'I is used to deflectwhich is in the form of a stepped sav/tooth. I

the beam of a cathode ray tube .in one Cartesian coordinate, such as for example, vertically. For v this purpose, the outputvof integrator I6 is connected to one set of deection plates I8 of a cathode ray tube I9, `whose other set of deflection plates 2il has a sawtooth voltage 2i applied thereto from a sawtooth lsweep circuit generator 22, the sawtooth generator 22 ybeing controlled by the markerpulse output from marker selector I2. The duration of sawtooth wave ZI is suilcient to include one stepped vertical sweep I'I for-each vertical row of target elements used. The'cathode ray tube I9 includes the usual electrongun 23 whichv is during operationfbiassed sof-that the beam is always turned on. The electron beam of tube I9 is swept across an aperture plate 24 which also servesas a collector electrode.- Behind the apertures of aperture plate 24 there is positioned a. plurality of secondary emissionl electrodes 25 similar inform to wave 'Il but with constant duration steps maybe used for the horizontal scan. i

,Since the pulses of curves A, B, and C are of the same amplitude, (and this may be insured by the use of limiters and shaping circuits, not shown), the rise v2t of each of the steps -ofwave- 4form il' willA be equal. Consequently, deection plates I8 will deflect the beam a constant amount from lstep to step sincethe amount of this deiiection is determined by the height of the rises 2S.

The `beam will be moved at each r-ise from" one oiv the target elements 25 to the next one'in `the same row. The length of time the beam'will remain'at each ofthe target elements is determined by the duration of the tread portions 2l. duration ofthe.k tread portions `2'I v-will depend upon the time modulation of the pulses.

Analysis of a single signal pulse and itstwo 'adjacent xed pulses =will `indicate the eiect of the time modulation-ofthe signal pulse upon the wave-form I'I and upon the deflection -o'fy the beam. For example, considering pulse 4 and its adjacent xed pulses hereinafter lspecifically designated by the

numerals

28 and 29, it will be seen that rises 3Q and 3| will occur at times iixed :by the

fixed pulses

28 and 29, Whereas the rise v3,2, -due to pulse'4, will vary, consequently varying the Vrespective lengths lof treads 133 and` 34.v For The ' f arrangement may be an'amplier.

4 example, if pulse 4 isf at one extreme of modulation 4a, its rise 32 will be moved to position 32a consequently making tread 33 considerably shorter than tread 34. When pulse 4 is at its other extreme of modulation, 4b, the rise 32 will be at position 32h and tread 33 will be much longer than tread 34. As has been stated before, the effect of different lengths or duration of the treads is to determine the length of time during which the beam lingers on a given target element Succeeding elements 25 in each row are to a push-pull arrangement 36, which push-pull The voltage output of the target elements, since they are secondary emission electrodes, is proportional to the Ulength of time that the spot remains on said elements. As indicated above, the length of time thespot remains on one target element of. an associated pair varies inversely with respect to the length: ottime it remains on the otherelement offsaidpair'N -Thus the elements of each pair are placed in a. push-pull relation and there is avreinforcement.- of` their potentials and an addition oi .theirrespective voltage cha-nges in the. push- .pull amplifier to. which they are connected vThe outputJQf-asaid. amplifier may be fed to any suitable utilization device 31 which may be for example, a soundfreproducer. n f l n y Succeeding pairs of thetargetelementsin each row are likewise connected to push-pull ampliersand. utilizationdeyices, each such push-pull amplifier andV utilizationv device serving as a sepalrate channel to which the signal information in- -tendedior said channelis fedi.,

vby having the dischargecircuit operate morel than once for each. series of pulses.

Numerous other ch anges `from ,the foregoing; description will read ilyrsuggest themselves to those versed in the art.

-Accordingly,..whi1e I. have described above the principles of. my `invention in connection. with specific, apparatus. itv yis .to be clearly Aunderstood thatv this; descriptionismade' only by way of` example--and not asali-mitation cnthescope oil my invention.

I.,claim;:, 1;. In a-.demodu'latcr system for multi-channel time modulated pulses including a synchronizing signal, a cathode ray tube having target-'elements ycdi-respending: to separate. channels, means for deecting the beam in said tube successively :across said; target-elements, and means controlling, in synchronism with the average repetition 4rate-of 'the synchronizingsi'gnal, deflection of the beam, and responsive to the time modulation of the pulsesqfor varying. the length ottime that said beamv is` directed at eachzfof said target elements.

2. In a channel separator and demedulatorvfor rmilti--channel=, pulse communication systems. of

.thetype in whichsa vplurality of channels are. in v'te-rleayedin sequence in the:-form of a: single mul,- -tiZ-cha-nnel-pulse Itrain,-` with one of .sa-id channels having-.pulses provideduvwithian- -i'dentifying- Vchars acter'istic distinct from the pulses of the other channels for use as synchronizing pulses, and the pulses of at least a given one of said channels being time modulated signal pulses; a cathode ray tube having a plurality of target elements, means for producing from a series of said pulses a sweep wave of stepped Wave-form, and means responsive to said wave for deflecting the beam in said tube across said target elements at a speed varying in response to the variation of the time modulation of said pulses.

3. In a 4channel separator anddemodulator for multi-channel pulse communication systems of the type in which a plurality of channels are interleaved in sequence in the form of a single multi-channel pulse train, with one of said channels having pulses provided with an identifying characteristic distinct from the pulses of the other channels for use as synchronizing pulses, and the pulses of at least a given one of said channels being time modulated signal pulses; a cathode ray tube having a plurality of target elements, means for integrating a series of said pulses to produce voltages having a stepped Wave-form, and means responsive to the voltages of said Wave-form to deect the beam in said tube across said target elements, whereby the length of time said beam is directed at a given target element varies in accordance With the time modulation of the pulses.

4. A system according to claim 3 further including means for beginning a new Wave-form with the next series of said pulses.

5. In a channel separator and demodulator for multi-channel pulse communication systems of channels for use as synchronizing pulses, and pulses of at least a given one of said channels being time modulated signal pulses; a `Cathode ray tube having a plurality of target elements, means for selecting the synchronizing pulses, means responsive to said synchronizing pulses for producing a plurality of pulses fixed in time with relationship to each other, means for interleaving said xed pulses between the incoming channel pulses, means for integrating the resultant output to produce voltages having a stepped Waveform, means responsive to said voltages for deflecting the beam in said cathode ray tube across said elements, the time modulation of the channel pulses determining the length of time at which the beam is directed at a given target element, means connecting pairs of succeeding target elements in push-pull, and suitable utilization means coupled to the output of said push-pull means.

6. A system according to claim 3 in which said target elements are arranged in a group of rows, and further including a sweep circuit generator controlled by said synchronizing pulses for periodically deiiecting the beam from row to roW for each succeeding stepped Wave-form.

7. A system according to claim 3 in which said target elements are secondary emission electrodes,

n said tube further lincluding collector means.

the type in which a plurality of channels are interleaved in sequence in the form of a single' ARNOLD LESTI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,189,898 Hartley Feb. 13, 1940 y2,263,369 Skillman Nov. 18, 1941 2,265,216 Wolf Dec. 9, 1941 2,395,467 Deloraine Feb. 26, 1946